Nonaqueous dispersed resin particles being used as a liquid developer for electrostatic photography, a printing ink, a coating material, etc., are the particles of a resin capable of fixing the coexisting pigment or dye as a film thereof and are required to be fine particles and stably dispersed. In particular, since the resin particles dispersed in a nonaqueous solvent having a high electric resistant give influences on image qualities of the developed images, the dispersed resin particles are required to have a good dispersibility.
As a process of producing the nonaqueous dispersed resin particles, a so-called nonaqueous dispersion polymerization reaction wherein a monomer which is soluble in a nonaqueous dispersing solvent and becomes insoluble upon polymerization is granulated by a polymerization reaction in the nonaqueous dispersing solvent and in the presence of a dispersion stabilizing resin soluble in the solvent to provide a nonaqueous resin dispersion containing the particles, is known and various processes are proposed, for example, in K. E. J. Barrett, Dispersion Polymerization in Organic Dedia, published by John Wiley & Sons, 1975; Sooichi Muroi, Cho Biryushi Polymer no Saisentan Gijutu (Highest Technology of Super Fine Particle Polymer), Chapter 2, published by C M C K.K., 1991; etc.
According to the nonaqueous dispersion polymerization reaction, the improvement of productivity such as saving of energy consumption, simplification of steps involved, etc., is attained and a particle dispersion having preferred characteristics such as fine particle sizes and a narrow particle distribution can be obtained as compared to a so-called mechanical process through kneading, grinding, and wet dispersion steps.
However, when bonding of the soluble dispersion stabilizing resin and the insoluble dispersed resin particles is insufficient, the dispersion stabilizing resin tends to diffuse in the solution, whereby the dispersion stabilizing resin is released from the resin particles after storage or repeated use of the resin particle dispersion for a long period of time, causing precipitation, aggregation, and using such dispersed resin particles for a liquid developer, since the resin particles once aggregated and accumulated are reluctant to redisperse, the particles attach to everywhere of a developing machine, which results in staining of images and machine troubles of the developing machine such as clogging of a liquid-sending pump, etc.
For overcoming these defects, a means of chemically bonding the soluble dispersion stabilizing resin and insoluble latex particles is proposed as disclosed in U.S. Pat. No. 3,990,980.
That is, according to the disclosed process, dodecyl methacrylate is copolymerized with glycidyl methacrylate having a polymerizable double bond group to synthesize a random copolymer soluble in a nonaqueous solvent, esterifying the random copolymer by a high-molecular reaction with methacrylic acid to provide a dispersion stabilizing resin having introduced therein a methacryloyloxy group, and subjecting the dispersion stabilizing resin to a polymerizing gradulation reaction.
However, in a liquid developer using the dispersed resin particles thus obtained by the foregoing process, the dispersion stability to the spontaneous precipitation of the dispersed resin particles is improved to some extent but the improvement is yet insufficient. When the liquid developer containing the dispersed resin particles is used for a developing apparatus, there is a problem that the liquid developer is insufficient in redispersion stability to put in practical use, such that the toners (dispersed resin particles) attached to each part of the developing apparatus are solidified in the form of film, which is not liable to redisperse and further causes machine troubles, staining of copy images, etc.
Also, in the production process of resin particles described in the foregoing U.S. patent, for producing monodisperse particles having a narrow particle distribution, there is a great restriction on the combination of a dispersion stabilizing resin being used and a monomer being insolubilized, and in general, resin particles having a wide particle distribution containing a large amount of coarse particles or polydisperse resin particles having at least 2 mean particle sizes are formed. Also, in the production process, it is difficult to obtain monodisperse resin particles having a narrow particle distribution and a desired mean particle size, and large resin particles having particle sizes of at least 1 .mu.m and very fine resin particles having particle sizes of smaller than 0.1 .mu.m are formed. Furthermore, in the foregoing production process, there is a problem that the dispersion stabilizing resin being used must be produced by a complicated production process requiring a long period of time.
For solving these problems, a process of using the dispersion stabilizing resin obtained by a process wherein in the polymer as described above, the polymerizable double bond group being bonded to the polymer of the dispersion stabilizing resin is bonded parting from the polymer main chain with at least 10 total atoms such that the copolymerization reactivity with the monomer which becomes the dispersed resin particles by being solubilized is not sterically hindered (e.g., U.S. Pat. No. 4,618,557 and JP-A-60-185962 ("JP-A" as used herein means an "unexamined published Japanese patent application")), a process of introducing the polymerizable double bond group to one end only of the polymer main chain of the soluble polymer (e.g., JP-A-1-282566), etc., is disclosed.
As described above, it is important that in the nonaqueous dispersed resin particles having a good dispersion stability, the dispersion stabilizing resin is efficiently bonded to the component becoming an insoluble resin by causing a reaction in the polymerizing granulation reaction such that they are not separated even in a severe using condition.
In the conventional known process as described above, the polymerizing granulation of a dispersion stabilizing resin and a monomer is carried out by adding thereto a polymerization initiator in a nonaqueous solvent.
For example, in the case of a radical polymerization reaction using an azobis compound, a peroxide compound, etc., as is known, since the stability of the initiation radical and the growth radical is low, the elemental reactions (e.g., recombination, chain transfer, stop, hydrogen abstraction, etc.) of a polymer proceed complicatedly, which results in making it difficult to attain efficient bonding of a resin component for a dispersion stability and an insolubilized resin component or forming gelled materials by the progress of a polymerization reaction.
Also, in an ionic polymerization reaction using a ionic polymerization initiator such as an alkyl metal compound, a Lewis acid, a Grignard reagent, etc., since the initiator and a growth living polymer react with an active hydrogen compound such as water, etc., to lose the initiating faculty, there is a problem that a severe purification of a solvent, monomers, etc., is required or the kind of the monomer forming resin particles is restricted.